Christophe Gadea has defended his PhD, showing that inkjet-based processing methods can be used for fabrication of thin films for energy devices like polymer solar cells and solid oxide fuel cells (SOFC)

Many energy technologies like polymer solar cells and solid oxide fuel cells (SOFC) are based on components made of thin, functional layers, with thinner layers providing enhanced performances. This makes reproducible, industrially scalable and low-cost production techniques very attractive when making thin films. Inkjet printing using a slightly modified standard printer has become a promising solution.

Four years ago development engineer Christophe Gadea and his colleagues at DTU Energy transformed an ordinary ink jet printer into a printer able to print thin films for energy conversion devices such as SOFC, significantly reducing the cost and the design-prototype-test cycle time for development of SOFC designs.

Challenge accepted

“We were able to print a functional oxide based thin film layer of one micrometer using a redesigned, but quite ordinary 20 dollar HP 1000 ink jet printer. That was groundbreaking news four years ago and led to many citations”, says development engineer Christophe Gadea, who tinkered with the printer.

"We were able to print a functional oxide based thin film layer of one micrometer using a redesigned, but quite ordinary 20 dollar HP 1000 ink jet printer"

Christophe Gadea,development engineer at DTU Energy

“I am specialized in ceramic materials and I like computer-based technologies, so I took it as a challenge.”

Christophe Gadea has now spend three years refining and further developing the techniques, and recently he successfully defended his thesis on “Smart nano-inks for inkjet printing of functional oxide based thin films” at DTU Energy.

Inkjet printing is a material deposition method based on the jetting of very small droplets (approx. 10-12 l) onto substrates. A maskless, non-contact additive patterning technique, it allows deposition of complex patterns with high positional accuracy of the droplets (≈ 5µm spacing) with high speed and low cost, using specially designed inks containing specially designed materials for the thin film fabrication.

The pros and cons of inks

“One critical aspect in inkjet printing is the ink design and its stability in the long term. Instability can lead to undesirable nozzle clogging and unresolved printing that lower the global performance of the device”, says Christophe Gadea, who evaluated the printability and the stability potentials of three different ink designs for inkjet printing in his thesis, as well as the pros and cons of each of them.

“The most promising result was a sol-gel, a solution that reacts with water forming small nanoparticles in the process, which is very useful in ceramic processing. When adapted to an inkjet-printer you can control the reaction”, says Christophe Gadea, who fabricated films made of zirconium- and titanium-oxide based materials with the inkjet-printers, using different droplet ejection principles to demonstrate the inks.

“I graduated as an engineer eight years ago from the National College for Engineering in Industrial Ceramics in France, so it took some changes to go back to the school bench and do a PhD, but it was worth it and it sure helped having both work experience and hands-on knowledge of materials”, says Christophe Gadea.

Before, Christophe Gadea always thought that without engineering, science was just philosophy. Now, having journeyed the realm of research and finished his PhD, he knows that both are equal partners.

“I belong in the lab solving problems, but I have become more systematic, more structured in my approach and I am not rushing to the lab whenever I get an idea anymore. I have learned to check the literature and maybe look for other solutions first. I think having two different views on problem solving is really good.”

Christophe Gadea has now returned to his job as a development engineer at DTU Energy, as was always the plan, working with alkaline electrolyzers for hydrogen production.

At the Department of Energy Conversion and Storage we work on sustainable energy technologies. In the energy system of the future a large part of the energy will be supplied by fluctuating sources such as solar and wind power. This makes it critically important to be able to convert and store the energy as needed.